In the medical field, various types of implantable leads are known and used. Particularly in the field of pacemakers, the use of implanted, transvenous pacing and/or sensing leads is very common. Pacemakers are typically implanted either in or outside the thoracic cavity, for example, under the skin near the patient's right clavicle, or in the patient's abdomen. An endocardial pacemaker lead, having a proximal end electrically coupled to the pacemaker and a distal end disposed within a chamber of the heart, conducts stimulating pulses from the pacemaker's pulse generator to the patient's heart, and/or conducts electrical cardiac signals from the patient's heart to the pacemaker's sensing circuitry.
One advantage of modern pacemaker systems is that the implant procedures are relatively simple and atraumatic, involving only a minimal amount of invasive surgery. The implant procedure can be performed under local anesthesia. Typically, an endocardial lead is introduced into the patient through a small incision at or near the implant site, usually just below and slightly medial to the junction of the middle and inner third of the clavicle. The distal end of the lead is first introduced into the patient's subclavian vein using any one of various introducer techniques known in the art. Then, the implanting physician directs the distal end of the lead through the vein and into the heart, by manipulating the proximal end of the lead. Once the lead is positioned, the proximal end is connected to the pacemaker. A somewhat larger incision is then made at the implant site, allowing the pacemaker to be inserted under the skin.
Pacemaker leads typically comprise a one or more coiled conductors surrounded by a resilient, bio-compatible insulative coating of silicon rubber or polyurethane. One or more pacing or sensing electrodes are disposed at or near the distal end of the lead body, and a connector pin for connection to the connector block of a pacemaker is disposed at the proximal end of the lead body. The insulated conductor is coiled to enhance the flexibility of the lead body and to reduce the possibility of metal fatigue and consequent lead failure due to flexing of the lead. The flexibility of the lead, while desirable from the standpoint of patient safety and comfort, makes the process of inserting the lead into the patient's heart somewhat difficult.
In order to facilitate the introduction of a lead into the patient's heart, a so-called "stylet" can be employed. As would be known to one of ordinary skill in the pacemaker art, a stylet is a relatively stiff wire that may be used during the lead implantation procedure to give the lead increased rigidity. In order to use a stylet, the connector pin of the pacemaker lead must be designed to permit insertion of the stylet into the cylindrical bore, or lumen, defined by the coiled lead conductor. The stylet can thus be inserted axially into the lead from the connector end and pushed into the lead so that the stylet runs along its entire length, increasing the lead's rigidity during the introduction procedure. A knurled end-piece disposed on the proximal end of the stylet allows the physician to manipulate the lead and navigate the distal end of the lead through the patient's venous system to the heart, by pushing and twisting the stylet. Once the lead is positioned, and before the lead is coupled to the pacemaker, the stylet is withdrawn from the lead, thus restoring the lead's flexibility.
Often, the physician will impart a curve to the stylet, so that after insertion of the stylet into the lead, the curve is imparted to the lead itself. The curvature of the stylet, and hence the lead, can facilitate the navigation of the lead through the venous system. For example, a curve near the distal end of the stylet (and thus, near the distal end of the lead as it is being introduced), can help the physician direct the lead around curves or corners in the subclavian vein. Once in the heart, the curved stylet can help to direct the distal tip of the lead to various structures within the heart, e.g., to the coronary sinus, to the atrial appendage, or across the tricuspid valve to the right ventricle.
In the prior art, the techniques used for imparting a curve to a stylet have been relatively primitive. For example, the physician may draw the stylet around the cylindrical body of a syringe, or around the edge of some surgical instrument, while keeping the stylet in contact with the syringe body or surgical instrument by pressing on the stylet with a thumb or finger. Such impromptu techniques, although commonly practiced, are deemed by the inventor to be undesirable for several reasons. First, it is important for the entire surface, and especially the distal tip of the stylet, to be smooth and free from kinks, sharp edges, or burrs that could damage the coiled lead conductor as the stylet is being inserted into or withdrawn from the lead. If an object that is too hard or that has sharp edges is used in the formation of a curve in a stylet, the stylet may be abraded or otherwise damaged. Abrasions on the stylet may make insertion of the stylet into the lumen of the lead difficult or impossible. Also, it is difficult to maintain constant contact between the stylet and the forming object with only a thumb or finger; this is particularly true at the extreme distal end of the stylet. If the stylet is not kept in contact with the forming body all the way to its distal end, the distal end may be irregularly curved.
A second perceived deficiency such improvisational prior art techniques for stylet forming may be difficult to repeat with consistent results; thus, a physician who discovers a particularly suitable and effective stylet formation may not be able to consistently reproduce such a formation.
It is believed by the inventor, therefore, that it would be desirable to provide physicians with an improved means for imparting a curve to a stylet. In particular, it is believed that there is a need for a stylet forming technique which does not damage the stylet, and which is repeatable with consistent results.